Evaluation of carbonyl sulfide biosphere exchange in the Simple Biosphere Model (SiB4)

Evaluation of carbonyl sulfide biosphere exchange in the Simple Biosphere Model (SiB4)

The uptake of carbonyl sulfide (COS) by terrestrial plants is linked to photosynthetic uptake of CO2 as these gases partly share the same uptake pathway. Applying COS as a photosynthesis tracer in models requires an accurate representation of biosphere COS fluxes, but these models have not been exte...

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Bibliographic Details
Published in:Biogeosciences Vol. 18; no. 24; pp. 6547 - 6565
Main Authors: Kooijmans, Linda M. J, Cho, Ara, Ma, Jin, Kaushik, Aleya, Haynes, Katherine D, Baker, Ian, Luijkx, Ingrid T, Groenink, Mathijs, Peters, Wouter, Miller, John B, Berry, Joseph A, Ogée, Jerome, Meredith, Laura K, Sun, Wu, Kohonen, Kukka-Maaria, Vesala, Timo, Mammarella, Ivan, Chen, Huilin, Spielmann, Felix M, Wohlfahrt, Georg, Berkelhammer, Max, Whelan, Mary E, Maseyk, Kadmiel, Seibt, Ulli, Commane, Roisin, Wehr, Richard, Krol, Maarten
Format: Journal Article
Language:English
Published: Katlenburg-Lindau Copernicus GmbH 22-12-2021
European Geosciences Union
Copernicus Publications
Subjects:
Agricultural land
Atmospheric models
Biosphere
Boundary conditions
Carbon
Carbon cycle
Carbon dioxide
Carbonyl compounds
Carbonyl sulfide
Carbonyls
Coniferous forests
Crop fields
Deciduous forests
Ecosystems
Environmental Sciences
Estimates
Fields
Fluxes
Gases
Grasslands
Growing season
Phenology
Photosynthesis
Representations
Respiration
Seasonal variability
Seasonal variation
Seasonal variations
Seasons
Soil
Soil fertility
Soil improvement
Soils
Sulfides
Sulphides
Terrestrial environments
Tracers
Uptake
Vegetation
Wheat
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Summary:The uptake of carbonyl sulfide (COS) by terrestrial plants is linked to photosynthetic uptake of CO2 as these gases partly share the same uptake pathway. Applying COS as a photosynthesis tracer in models requires an accurate representation of biosphere COS fluxes, but these models have not been extensively evaluated against field observations of COS fluxes. In this paper, the COS flux as simulated by the Simple Biosphere Model, version 4 (SiB4), is updated with the latest mechanistic insights and evaluated with site observations from different biomes: one evergreen needleleaf forest, two deciduous broadleaf forests, three grasslands, and two crop fields spread over Europe and North America. We improved SiB4 in several ways to improve its representation of COS. To account for the effect of atmospheric COS mole fractions on COS biosphere uptake, we replaced the fixed atmospheric COS mole fraction boundary condition originally used in SiB4 with spatially and temporally varying COS mole fraction fields. Seasonal amplitudes of COS mole fractions are ∼50–200 ppt at the investigated sites with a minimum mole fraction in the late growing season. Incorporating seasonal variability into the model reduces COS uptake rates in the late growing season, allowing better agreement with observations. We also replaced the empirical soil COS uptake model in SiB4 with a mechanistic model that represents both uptake and production of COS in soils, which improves the match with observations over agricultural fields and fertilized grassland soils. The improved version of SiB4 was capable of simulating the diurnal and seasonal variation in COS fluxes in the boreal, temperate, and Mediterranean region. Nonetheless, the daytime vegetation COS flux is underestimated on average by 8±27 %, albeit with large variability across sites. On a global scale, our model modifications decreased the modeled COS terrestrial biosphere sink from 922 Gg S yr−1 in the original SiB4 to 753 Gg S yr−1 in the updated version. The largest decrease in fluxes was driven by lower atmospheric COS mole fractions over regions with high productivity, which highlights the importance of accounting for variations in atmospheric COS mole fractions. The change to a different soil model, on the other hand, had a relatively small effect on the global biosphere COS sink. The secondary role of the modeled soil component in the global COS budget supports the use of COS as a global photosynthesis tracer. A more accurate representation of COS uptake in SiB4 should allow for improved application of atmospheric COS as a tracer of local- to global-scale terrestrial photosynthesis.
ISSN:1726-4189
1726-4170
1726-4189
DOI:10.5194/bg-18-6547-2021